This invention relates to poly(hydroxy acid)/polymer conjugate formulations for cosmetic and dermatological skin applications, and methods of use thereof.
Skin disorders range from various cosmetic conditions to severe dermatologic diseases. Conventional treatments for many of these disorders have included topical applications of oils, emollients, humectants, drugs and medicaments. Such treatments have met with varying degrees of success.
It is also known to use hydroxy acids, especially alpha and beta hydroxy acids, in the treatment of various skin conditions, for example, as reviewed in U.S. Pat. Nos. 5,091,171 and 4,363,815 to Yu and Van Scott, which describe the use of various hydroxy acid monomers and oligomers (containing two or three units) in skin treatment. Other patents relating to skin treatment with hydroxy acids include U.S. Pat. Nos. 3,988,470, 4,105,782, 4,234,599, 4,380,549, and 5,258,391. Others describing the use of hydroxy acids in skin treatment include EP 0 358 528 by Periera, U.S. Pat. No. 4,294,852 to Wildnauer et al., and U.S. Pat. No. 2,726,982 to Ochs.
While hydroxy acids are well-known in skin treatment, there are various problems inherent in their application to skin, especially from the point of view of safety. In particular, use of a formulation which contains free monomeric hydroxy acids results in an immediate one-time introduction of the full dosage upon application to the skin, which can cause peeling, chemical burning and even scarring of the skin. This problem is specially acute with the more concentrated doses described in the Yu et al patents, referred to above.
In principle, this problem can be overcome by polymerization of the hydroxy acids (HAs) to form polyhydroxy acids (PHAs). Polyhydroxy acids such as polylactic acid, polyglycolic acid, are polycaprolactone are well-known in the manufacture of degradable medical devices, such as sutures (for example, Vicryl.RTM.), absorbable sponges and fabrics, and other devices. They are suitable for such uses because PHAs become water-insoluble at relatively low degrees of polymerization. The polyhydroxy acids gradually degrade back to the monomeric acids in the presence of water or of bodily fluids at approximately neutral pH. The principal drawback of these materials is a mild degree of irritation or inflammation at the site during the degradation of the polymer. This is acceptable in the context of wound repair, but is less acceptable in treatment of the skin for relief of cosmetic problems.
Moreover, it is difficult to eliminate this effect by dissolving or dispersing the PHAs in solvent. It is known that polyhydroxy acids such as polyglycolic acid are not soluble in skin-compatible solvents, but only in organic solvents such as hexafluoroacetone hexahydrate or hexafluoroisopropanol, acetone, and methylene chloride. Attempts to disperse pure PHAs in other components of a cosmetic formulation are thus difficult, and could lead to phase separation of a PHA-rich phase within the formulation, leading to gradations of different concentrations of the hydroxy acid on the skin to which the formulation is applied.
It is therefore an object of the invention to provide a safe, effective and easy method for alleviating the symptoms of a cosmetic or dermatologic skin condition.
It is a further object of the invention to provide a method for the controlled release of hydroxy acids onto the skin of a person to alleviate the symptoms of a cosmetic or dermatologic skin condition.
It is another object of the invention to provide a method for alleviating the symptoms of a cosmetic or dermatologic skin condition which combines the advantages of a humectant and an hydroxy acid.
It is a still further object of the invention to provide a method for alleviating the symptoms of a cosmetic or dermatologic skin condition by providing a formulation which results in substantially uniform application of hydroxy acids to the skin.